feat: Google Photos provider backend + API hardening

- Add Google Photos provider: client, models, change detector, capabilities
- Add notification templates (en/ru) for all GP event slots
- Add command templates (en/ru) for GP bot commands
- Register GP in slot/command loaders, capabilities, and seeds
- Harden provider API: validate OAuth credentials on create/update
- Add internal URL rewriting for asset fetches (LAN optimization)
- Fix template renderer to handle missing variables gracefully
- Improve webhook command routing for multi-provider support
- Add provider health check endpoint and watcher improvements

packages/server/src/notify_bridge_server/database/seeds.py

@@ -152,6 +152,7 @@ async def _seed_default_templates() -> None:
         await _seed_provider_template(session, "planka", "Planka")
         await _seed_provider_template(session, "scheduler", "Scheduler")
         await _seed_provider_template(session, "nut", "NUT")
+        await _seed_provider_template(session, "google_photos", "Google Photos")
         await session.commit()
 
 
@@ -175,6 +176,9 @@ async def _seed_default_command_templates() -> None:
         await _seed_provider_command_template(
             session, "nut", "Default NUT Commands", "Default NUT command templates",
         )
+        await _seed_provider_command_template(
+            session, "google_photos", "Default Google Photos Commands", "Default Google Photos command templates",
+        )
         await session.commit()
 
 
@@ -305,6 +309,16 @@ async def _seed_default_command_configs() -> None:
                 "default_count": 5,
                 "rate_limits": {"api": 15, "default": 10},
             },
+            {
+                "provider_type": "google_photos",
+                "name": "Default Google Photos",
+                "enabled_commands": [
+                    "help", "status", "albums", "latest", "search", "random",
+                ],
+                "response_mode": "media",
+                "default_count": 5,
+                "rate_limits": {"search": 30, "default": 10},
+            },
         ]
 
         for cfg in defaults: